Telephone system



Jan. 7, 1947. R. E. HERsEY 2,413,708

TELEPHONE SYSTEM Filed Nov. 9, 1944 '7 sheets-sheet 1 CONTROL 'F/c;` a

FIG 2 FG J F76 4 FIGS F/ 6 FIG. 7

CALLED LINK CONTIWJLl CKT TTNE V Jan. '7, 1947. R. E. HERsl-:Y

TELEPHONE SYSTEM Filed Nov. 9. 1944 7 Sheets-Sheet 2 QC U. E NLI SNE; E. 11|/ /Nl/ /v By R; EHESEV Q We Jan. 7, 1947. R, E HERSEY 2,413,708

. TELEPHONE SYSTEM Filled Nov. 9, 1944 7 Sheets-Sheet 3 LINK ck: l

L//wr cfrr z /NVENTOR R E HERSEV ATTO/NE V R. E. HERSEY TELEPHONE SYSTEM v '7 sheets-sheet 4- Filed Nov. 9, y1944 /Nl/E/v R. E HERSEY 5r IIIIII ATTORNEY Jan., 7, 1947. -R. E. HERsEY vTELEPHONE SYSTEM File-d Nov. 9, 1944,

'T Sheets-Sheet 5 ATTORNEY Jan. 7, 1947. R. E. HJERsEY 2,413,708

TELEPHONE SYSTEM Filed Nov. 9, -1944 7. sheets-sheet s FIG. 6

LINK CONTROL CIU.'

/NVEM R By R 5 HERSEY l @Mya/49e.

l A ATmAr/vfeyv Jan. 7, 1947.

R. EJ HERSEY TELEPHONE SYSTEM 7 Sheds-Sheet 7 Filed Nov. 9, 1944 /NVENTOR A R E HERSEY Q61 Ok A TTORNE Y Patented Jan. 7, 1947 .,PATEN T orifice TELEPHONE SYSTEM Ralph E. Hersey, Madison, N. J., assigner to Bell Telephone Laboratories,

Incorporated, New

York, AN. Y., a corporation of New York Application November 9, 1944, Serial No. 562,598

This invention relates to telephone systems and particularly to systems in which cross bar switches are employed to automatically establish connections between subscribers lines.

An object is to simplify and improve the operating characteristicsV of systems of this kind and to reduce the individual equipment required for the subscribers lines and to reduce and utilize to the fullest extent such common equipments as are required for controlling the establishing of connections between subscribers lines.

Heretofore cross bar switches have been used in small capacity systems for establishing connections between subscribers over interconnecting links by the aid of control relay groups or marker circuits and minor switches which select and operate the individual select and hold magnets in such switches.

The present invention relates to small capacity systems of this general type and an inventive feature thereof is an arrangement of a so-called Calling line cross bar switch and a called line cross bar switch in which each subscribers line appears once in each switch and interconnecting links which appear in both switches for the connection of calling lines with called lines. A common marker circuit is provided and operative when a subscriber calls for identifying the calling line in the calling line switch, for seizing an idle linkl and for extending a pulsing circuit from the calling line relay through this marker circuit to minor switches. Said minor switches in turn are responsive to dial pulses received over said pulsing circuit, to select any called line in the called line switch. Additional circuits are also provided and connected through said marker circuit and minor switches for thereafter establishing a connection between a calling subscribers line and a called subscribers line through said switches over the chosen link.

Another feature is an arrangement whereby the line relay of the called subscribers line serves as a ringing trip relay.

Another feature is an arrangement whereby the talking battery for the calling line and for the called line is supplied through their respec- 'tive line relays.v These circuits are also arranged to eliminate the use of cut-oli." relays: The invention has'been illustratedrin the accompanying drawingsy in which Fig. 1 showsf in diagrammatic vform a typical arrangement ofthe applicant-s invention in a system employing the two' switches; while-Figs. 2 to '7 when arranged in accordance with Fig. 8, illustrate vin more detail the applicants invention with the circuits re- 1 Claims. (Cl. 179-22) quired for the establishing of a'connection bef tween a particular calling subscribers line and a particular called subscribers line.

Reference is now made to the drawings and particularly to Fig. 1 where the general plan is shown to indicate the calling line cross bar switch A and the called line cross bar switch B, and interconnecting links C and D vbetween said switches. The calling cross bar switch A is arranged with eight select magnets 200 to 2|l`| and switch B with eight select magnets 400 to 401 for selecting levels in-which subscribers lines appear and hold magnets 2|!) to 229 in switch A and hold magnets 4|IJ to 429 in switch B for connecting subscribers lines to vertical contact rows. In switch A are also shown two select magnets 23| and 232 for the two links C and D and similar select magnets 43| and 432 for these links in switch B. As stated, each subscribers line is represented once in each of these two switches and the numbering at the subscribers lines may beas follows. For example, the rst twenty subscribers O to 19 will be connected on the first level and succeeding numbers of subscribers in groups of twenty will be appearing in the succeeding eight levels so that, for example, in the eighth level the subscribers numbers to 159 will appear in the succeeding twenty rows in this level. That is to say, line 0 is represented at the cross-points 233 and 433 in switches A and B and avvertical contact rowy is provided for each hold magnet, for example, the vertical contact row 236 is provided for hold magnetv 2H) inV switch A and the vertical contact row 430' is provided for hold magnet 4|0 in switch B. Thus, if a connection is desired from subscriber 0 as a calling subscriber in switch A over the idle link C, for example, the connection will be` established at the cross-point 233 between the calling subscriber 0 and the contact row 230 and at cross-point 234 between this row 230 and link C, and similarly if a'connection is to be established between this link and, for example, subscriber 159, as the called subscriber, a connection is established through the cross-point 435 between link C and the row 436 and at the cross-point 431 between the row 35 ,and the subscribers line 159. This connection is effected by the operation of select magnets -Zil-and- 23| inswitch-A and select magnets 43| and 401 in switch B and the hold magnet 2|!) in switch A and hold magnet 429 in switch-B,

- 'Irhel control or-marker circuit and other circuit-s have been illustrated` diagrammatically in For example, E indicates the markery cir'- cuit with relays varranged in groups as follows:

One group comprises thirty-two relays marked T divided in eight sub-groups of four each and another group of thirty-two relays marked P divided in eight sub-groups of four each, while a group of iive relays is marked U and a;group of four relays is marked TT. These relays and their circuitsare for identifying and establishing connections in the calling switch A and for extending the pulsing circuits. For controlling the connections in the switch B, over the link C or D in switches A and B, a group of relays is provided and indicated by a box marked F. A minor switch G is provided for controlling the select magnets for the called subscribers line in switch B and minor switches H and I are provided for selecting the hold magnets inswitch B. The circuits for the line links C andD are indicated by a box marked K. The subscribers line relays, for the sake of clearness, may be considered as arranged in groups of eight associated with each vertical row of contacts. One group of eight line relays for lines 0, 20, 40, 60, 8()J 100, 120 and 140 ha-s been indicated at 240 and similar 'groups of groups are arranged for the succeeding vertical rows, that is 160 line relays would be arranged in twenty groups, the last eight relays for lines 19, 39, 59, 79, 99, 119, 139 and 159 being indicated at 24|.

A description will now be made in general in connection with Fig. l of how a connection is established between the calling subscriber and the called subscriber 159. When the calling subscribers line relay 500 is operated, the marker relays E will be operated as follows. For example, the relay 50| in the first sub-group of four in the P group will be operated causing the operation of the corresponding relay 502 in the first sub-group of four in the T group k,which causes the operation of relays 506 in group TT and 501 in group U, that is, these relays in operating indicate that the calling subscribers line is 1ocated in the lower or first horizontal level and in the rst vertical row; that the nrst select magnet 200 and the first hold magnet 2|0 should be operated and that the select magnets for an idle link should be operated in both switches A and B. What actually takes place when the subscriber calls due to the operation of the above-mentioned relays is that theselect magnet 200 is operated as well as the select magnets for an idle link, such as, for example, select magnets 23| and 43| for link C, if this link is idle. The abovementioned relays in the marker circuit E also extend a pulsing circuit 5|4 and a dial tone circuit 5|5 to the circuit arrangement F over these relays from the calling subscribers line relay 500. A dial tone will now be transmitted over circuit 5|5 to the calling subscriber indicating that he may begin to dial the desired number. If the subscriber 159 is desired, the rst digit dialed will be 8 to cause the switch G to select and operate select magnet 401 in the switch B to indicate that the called subscribers line is located in the eight level. The second digit will then be dialed and as the subscriber 159 is the'one desired, the switch H`will be operated to take two steps to select one of the switches l, to wit, the second switch as 'thei-subscribers line 159 is located in the second-'ori'rght-hand half section of switch B. The third impulse will then be dialedfor the operation ofVA the hold magnet 429. The circuit arrangement-fissuch-that at this time the hold magnet 2 !0.is"also operated. Thus. it will be seen that a connection is' now established from the subscriber 0 to the sub- 4 scriber 159 over link C through the cross-points 233 and 234 in switch A, and cross-points 435 and 431 in switch B. When this takes place, the circuit arrangement K common to links C and D will operate to apply ringing current to the called subscriber-s line and when the called subscriber answers this call, the ringing will cease and the talking connection through link C will be established between the two subscribers.

To perhaps describe in more detail the arrangement of the marker relays, it should be again noted in this Fig. l that the T and P relays are divided in eight sub-groups, each containing four relays and that a group of eight line relays is associated with each hold magnet. For example, the first eight line relays 240 are associated with the hold magnet 2|0 and in turn associated through contact of this hold magnet with the rst sub-group of four relays at the bottom of the groups T and P and also the rst or lower relay 501 of the U relays and 506 of the TT relays. Thus, U relays preselect one out of ve groups of hold magnets, each group consisting of four hold magnets and the TT relays determining the individual hold magnet to be operated in the preselected group. If it is assumed, for example, that the subscriber 45, located in the sixth vertical row and the third horizontal level is calling, the relays 508 and 509 of the third group of P and T relays and the second TT and U relays 5|0 and 5|| will be operated to indicate that the third select magnet 203 should operate to designate the level in which subscriber 45 is located and the sixth hold magnet 2|4 should be operated to indicate that the calling subscriber is located in the sixth vertical row to establish the connection for this subscribers line 45 through switch A at cross-point 245.

Referring now to Figs. 2 to '7, which show the system in more detail, a description ywill be made of a call from subscriber O to subscriber 159. Fig. 2 shows the calling switch A; Fig. 3 the circuits K for the two links C and D; Fig. 4 the called switch B; Fig. 5 the marker circuit E for the calling lines; Fig. 6 the link control circuit F and Fig. 7 the called line control switches G, H and I. If now the subscriber (l calls, the line relay 500 operates from battery and ground through the windings of this relay and the subscribers station loop. The operation of this line relay closes a circuit for the operation of P relay 50| in the marker circuit E from battery, winding of this relay, contact of T relay 502, contacts of hold magnet 2|!! and contacts of line relay 500 to ground. Relay 50| closes a circuit for relay 502 from battery, winding of this relay, contacts of relay 50| and 600 to ground. As the subscriber 0 is located in the lower or first level of the switches A and B, the select magnet 200 operates over an obvious circuit by the operation of relay 502. Relay 502 closes a circuit for the operation of TT relay 506 from battery, Winding of this relay, contacts of relay 502 to ground. The operation of relay 506 marks or signifies that the calling subscriber is one of the rst five subscribers lines terminating in the first or lower level in the switch A. Relay 502, in operating, also closes a circuit over its lower inner armature and front contact and through the winding of relay 60| through a resistance to battery at 602 causing relay 60| to operate. Relay 60| in operating closes a locking circuit for itself and also a locking circuit for relay 502 to ground at the right-hand armature and iront contact of this relay 60|.

1`Relay 60| in operating closes an obvious circuit for-relay 600 which, however, is slow to. operate to permitr relay 603 to operate iirst as will 4presently be described. It should be noted that if any of the other P relays have been operated at the i. time subscriber calls, the battery i503` would have been opened from relay Sill and consequently, prevents subscriber 0 from calling at this stageof the operation. Thus, if' relay 5M is operated' the battery 503 is cut off from the chain circuit leading to the other P relays. It should now be noted that relay the winding of this relay, contacts of relay 5322, contacts of ho-ld magnet 2in to ground at contacts of the line relay 50G. Relay 5B1 in operating closes at itsL upper armature and front contact a circuit for theoperation of the abovementioned relay dit@Y from battery through the winding of this relay, dial tone coil 6&5, lead 5|5, upper armature and front contact of relay '5B1 to the above-mentioned ground at the line relay 500'. This causes the operationy of relay 533, that is, relay Bil-3 operates before relay Sill) operates for reasons as will become apparent at the time of release of the. marker circuit. A circuit is 'now closed for the operation of thev select magnets of an idle link circuit, for example, if link C is idle and link D is busy a circuit will V.be completed from battery through the .select magnet 23| of switch A and also irombattery through the select magnet 43| of switch B, con- Hadl links C and D been busy, the busy relay 5|!) would have been operated from battery, winding of this relay, contacts of relay 3&6 of link D and 30| of link C to ground. Relay 6m in operating would have applied busy tone yfrom the source 5| I v through the tone coil Eil-5 over lead SI5 tothe calling subscriber .0. It willl be explainedl hereinafterhowrelays 3M! and 35H. of links C and D will be operated when these are. engaged.

If now it is determined that the cal-ling sub- L scriber desired to call subscriber 159, he must, of course, as the first digit, dial the digit 8 to reach the level in' which this called 'subscribers line is'located. With the line relay-593 serving as the, pulsing relay and with the pulsing circuit 5 extended through the .common pulsing lead 554, on the iirst release of the relay 530, a circuit is completed for the operation of the stepping magnet '|00 for switch G from battery through the winding of this magnet, contacts of relays 6|2 and 603, pulsing lead 5M, contacts of relays 5t? and 532 to ground at contacts of relay 539. Each relay 50.1 alsooperated `on .the operation of relay 502' from battery through a chain circuit from pulse will advance the switch one step. It should be noted also that the first impulse causedthe .operation of relay l over an obvious circuitfl and this relay operates relay 6|# from battery,

winding of this relay, contacts of relays SI2 andi Relay (S is maintained operated during.

.5!3. the succeeding pulses, as it isA slow in releasing; The magnet 76|] steps the brush of switch G to succeeding terminals until eight steps have beenY taken. Atthis time, relayv @i3 will release permittinsl relay 642 to operate overa circuit from battery overt-he-,winding of relays 8M and m2 .rcontacts of relays .EIA and. 6ii3 to ground. This opens the; pulsing circuit f or thev stepping. magnet |00 which nowr releases. The` operation of relay 6i'2ucloses a circuit over the brush of switch. G to operate select magnet 481 in switch B which thereby prepares this switch for the selectionV of a subscribers line in theeighth level. The arrangement of the switches H and I are such that the switch H will take one or two steps toestablish connections for the brushes in bank '|62- or '|93 for the selection and operation of hold `magnets in switch B in the iirst group of ten or in the second group of ten. As the second digit in this case will be 2A the called subscriber line being located in the second part of the switch B, the switching bank '|03 of switch I will be selected. These two impulses are received at the dialing of the second digit through the pulsing circuit now extended to stepping magnet '|04 for switch H over contacts of relays 6|2 and 6|5. As relay SIS is again operated on the receiving of the rst impulse, a circuit will at this time be completed for the operation of relayv 6 'l from battery, winding of this relay, contacts of relays SI5, 6|2 and 6|3 to ground. After these two impulses have been received and advanced the brush of switch H to the second position, relay 6i'3 releases and the circuit isnow completed for the operation of relay 6|5 from battery through the windings of relays BIT and lil-5, contacts of relays Ell and 8&3 to ground. The third digit will now consist of ten impulses as the twentieth hold magnet 429 must be operated in order to establish a connection in switch B for the subscriber 159. On

the first impulse of this last digit the pulsing circuit extends as before from the pulsing relay 5e!) over contacts of relays 562, 507, 603, 6|2 and Gi to the select magnet m5 for the switch I. Relay 6|3 is operated by this circuit and relay 62d is then operated from battery through the winding of this relay, contacts of relays 62|, 6|5, 5|2 and B13 to ground. rlhe stepping magnet '|05 will now be advanced to have its brush land on the tenth terminal in the two banks m2 and 163. At the end of this sei-ies of impulses, relay 6l3 will release and permit relay 621 to operate from battery through the Iwindings of relays 620 and: 52|', contacts of relay 62H and 663 to ground. The operation of relay 62| closes a circuit for the operation of the hold magnet 429' from battery winding of magnet 429, tenth contact of bank 763, second contact of switch contacts of relay 52|. tov ground. This causes a connection to be established'in switch B between the idle link C and the subscribers line 159 at the cross-points @-35 and Slover thevertical row of `contacts 435. rThe operation of relay 52| also closes a circuit for the hold magnet 2 It from battery through the winding of this magnet, contacts of relays 5236 and 62| to ground. Magnet 2 il now closes a connection between the vcalling subscriber over the vertical row of contacts 23D at the cross-points 233 and. 234 to link Cso that this link C is nov.' connected both to the calling subscriberfs line 0 and" the called subscribers line 159. The two hold magnetsl! 0 and 425 are now connected over the sleeve connection at cross-points 23S-and ZC-l and 35 and 153i to the ground at the line relay dtd' and held operated by this ground. It should be noted that this sleeve circuit also passes through a relay 30e in link' C which at the righthan-d end ofthis sleeve is connected to they ground at relay 560, and in the -link `ci-rcuit is connected to batteryfthrough the relay 36|. Relays and 30| will Anow operate from this ground. The operation ci?D this -reiay 36| releases select mag- 7 nets 23| and 43.! and closes a' connection from ground -to a contact of relay 300 so that if link D is busy, the associated busy relay SII] will opcrate to indicate that both links are busy.v The operation of relay 365 closes a connection from ringing interrupter 3H) through contacts of this relay and winding of the ringing relay 3H to battery. This relay 3H is thereby alternately operated and released to apply ringing Vcurrent to the tip and ring conductors at intervals overy `cease and the two subscribers lines are connected together through the condensers 312 and 3l3 for talking. As the hold magnet ZIO was operated, it should be observed that the pulsing circuit is broken at its armature and front contact for this line so that the ground will be removed from the circuit for relay 603 causing this relay to release. Relay 6s3 in releasing, applies ground at its right-hand armature which releases relay 60|. Relay 68| releases relay 690. then releases the marker circuit relays operated such as SEZ, which cause the release of relays il and 531 and the select magnetl 29S. Relay 683 also releases relays SI2, 6M, Ell, 6&5, 626 and EZI. Relay M2 causes the release of select magnet 487 and relay 62| opens the original energizing circuit for hold magnet', 429. Any wellknown arrangement may be provided for the release of switches G, H and I at this time. When the subscribers hang up relays 599 and SI release causing the release of hold magnets 2 l 0 and 1329 to release the connection through link C in which relay 301 is now released.

What is claimed ls:

1. In a telephone system, a calling cross bar switch, a called cross bar switch, subscribers lines each terminating in a correspondingly located cross-point in each of said switches, links between said switches, a line relay for each subscribers line, control means including a series of relays and minor step-by-step switches associated with said lines and links, operative in response to the seizure of a calling line and operation of the associated line relay in response to dial pulses for automatically establishing a .connection from the calling line to an idle link in the calling switch and selectively establishing a connection to the called line from said link in the called switch, ringing the called line and when the called' subscriber answers establishing a talking circuit over said link between the calling subscriber and the called subscriber and releasing said control means.

2. In -a telephone system, a calling cross bar switch, a called cross bar switch, said switches including select magnets and hold magnets, subscribers lines each terminating in a correspondingly located cross-point in each of saidswitches, links between said switches,` a line relay for each line, means responsive to the operation of asubscribers. line relay when the subscriber calls foroperatin'g-the select magnet in the calling switch for the level in which the calling line is located and the select magnets in both switches for the level in which a rirst idle" link is located land ,for

Relay Gili .2

marking the hold magnet in the calling switch for establishing subsequently -a connection between the calling line and said idle link, means responsive to the loperation and release of the line relay of the calling line in response to a rst digit dialed by the calling subscriber for actuating .the select magnet in the called switch for the level in which the called line is located, means responi sive to a second and a third digit on the actuaof the third digit the marked hold magnet in' the calling switch to connect the calling line to the idle link, and for selecting and actuating -a hold magnet `in the called switch representing the called line for connecting this called line to said link, means operative when said connection through the called switch is completed, for ringing the called lsubscribers line and releasing said select magnets and associated control means for use in establishing other connections through said switches, and means controlled by the called subscribers line relay when it operates in response to the called subscriber answering the lcall for tripping the ringing and establish a talking connection between the calling subscribers line and the called subscribers line through said switches over said link with the line relays of said subscribers lines holding the hold magnets operated.

3. In a telephone system, two cross bar switches, subscribers lines appearing in both switches, links appearing in and connecting both switches, a line relay for .each line, means responsive to the operation of a calling subscribers line relay on the seizing of the corresponding line for marking the connection between the calling line and an idle link in one switch, means thereafter responsive to the release and operation of said line relay in response to dial pulses for connecting said link to a called line in the other switch and when said connection is made for then connecting in accordance with said marking the calling line in the first-mentioned switch to said link and ringing the called line, means responsive to the operation of the line relay of the called line when the called subscriber answers the call for tripping the ringing and completing a talking connection.

through said link between said subscribers line with their respective line 'relays maintaining the connection.

4. In a telephone system, a calling cross bar switch, a called cross bar switch, subscribers lines each terminating at one position in each of said switches, a line relay for each subscribers line, an individual pulsing lead controlled by each line relay, interconnecting links having .an outgoing branch terminating in the calling switch and an incoming branch terminating in the called switch, vertical links in said switches, select magnets and hold magnets in said switches, means operative in response to a call from one of said lines for actuating two select magnets and marking a particular hold magnet in the calling switch for the subsequent connection of the calling line to a particular vertical link in the calling switch and a subsequent connection of said vertical link to the outgoing branch of an idle interconnecting link, and for actuating the select magnet associated VAwith the incoming branch of said interconnecting link for the subsequent connection of said incoming branch to a vertical link in the called switch, stepping switches, means for extending the individual pulsing circuit from the calling subscribers line relay to said stepping switches for the control thereof inresponse: to impulses transmitted by the calling subscribers line relay over said extended pulsing circuit to actuate a select magnet and a hold magnet corresponding to a called line in the called switch and to thereupon actuate the particular marked hold magnet in the calling switch to establish a connection from said calling line over a particular vertical link in the calling switch, over the chosen interconnecting link and a particular vertical link in the called switch to the called line, means thereafter responsive for ringing the called subscribers line and means responsive to the called subscribers answering said ringing for discontinuing the ringing and closing a talking connection through the chosen intermediate link between said calling subscribers line and said called subscribers line.

5. In a telephone system, a calling cross bar switch, a called cross bar switch each having select magnets and hold magnets, subscribers lines each terminating in both switches, links terminating in and connecting both switches, a line relay for each line, a pulse circuit for each line relay, a marking circuit including relays operatve in response to the operation of a line relay on the seizure of the corresponding line by a subscriber for operating a select magnet in the calling switch indicating the level in which the calling line is located, for operating select magnets in both said switches indicating the level in which the idle link is located in said switches and for marking the hold magnet in the calling switch, which when operated connects the calling line to an idle link, for extending the individual pulsing circuit of the calling line relay through said marking circuit, a common circuit including relays and mino-r step-by-step switches, said common circuit and step-by-step switches being so arranged as to respond to impulses transmitted over said eX- tended pulsing circuit by the operation and release of the calling subscribers.line relay for actuating the select magnet indicating the level in which the called line is located and for thereafter actuating a hold magnet in the called switch to connect the called subscribers line to said idle link and to actuate the particular marked hold magnet in the calling switch, to connect the calling line to said idle link and means operative on the operation of said hold magnet in the calling switch for releasing the common circuit and minor switches and marker circuit and for ringing the called line from this seized link and means whereby when the called subscriber answers the call by the operation of his line relay to trip the ringing and connect the calling line with the called line for talking over said seized 10 link, and means for holding said hold magnets operated under control of said line relays of the calling line and called line.

6. In a telephone system, a calling cross bar switch, a called cross bar switch, subscribers lines each terminating in a correspondingly located cross-point in each of said switches, links between said switches, a line relay and a source of current connected through said line relay for each subscribers line, control means including a series of relays and step-by-step switches associated with said lines and links operative in response to the seizure of a calling line and operation of the associated line relay from the associated source of current in response to dial impulses for automatically establishing a connection from the calling line to an idle link in the calling switch and selectively establishing a connection to the called line from said link in the called switch for ringing the called line and when the called subscriber answers by operating the called line relay from the associated source of current for establishing a talking connection over said link between the calling subscribers line and the called subscribers line with the respective sources of current through the corresponding line relays serving as the respective talking batteries for said lines and for releasing said control means.

7. In a telephone system, two cross bar switches, subscribers lines appearing in both switches, links appearing in and connecting both switches, a line relay and a source of current connected through said line relay for each line, means responsive to the operation of a calling subscribers line relay from the associated source of current on the seizure of the corresponding line for marking the connection between the calling line and an idle link in one switch, means thereafter responsive to the release and operation of said line relay in response to dial pulses for connecting said link to a called line in the other switch and when said connection is made for then connecting in accordance with said marking the calling line in the rst-mentioned switch to said link and ringing the called line, means responsive to the operation of the line relay of the called line from the associated source of current when the called subscriber answers the call forl tripping the ringing and completing a talking connection through said link and said line relays between said subscribers lines with the associated sources of current serving as talking batteries for the respective lines and with the said line relays holding the established connection.

RALPH E. HERSEY. 

